Use this recipe to make Martha's Spring Garden Cake.
Preheat oven to 350 degrees. Spread walnuts on a baking pan; bake until fragrant, about 7 minutes. Cool completely on a wire rack. Coarsely chop walnuts, and set aside. Lightly oil two 10-by-2-inch round cake pans, and line bottoms with parchment. In a medium bowl, sift together flour, cinnamon, baking powder, and salt. Set aside.
In the bowl of an electric mixer fitted with the paddle attachment, combine oil and sugar on low speed. Slowly add half of the flour mixture, and continue mixing until well blended. Add remaining flour mixture and eggs in three additions, beginning and ending with the flour mixture. Mix until combined, about 1 minute.
Transfer batter to a large mixing bowl. Stir in carrots, orange zest, and walnuts. Divide batter equally between prepared baking pans (6 1/2 cups per cake pan for the carrot and 6 cups for the zucchini). Bake until golden brown and firm, about 1 hour. A wooden skewer inserted in the center of the cake should come out clean.
Transfer pans to wire rack to cool completely before unmolding.
You can also use 9-by-13-inch baking pans to make this cake.
To make the zucchini cake, substitute 6 cups grated zucchini (about 1 3/4 pounds) for the carrot, omit the orange zest, and add 2 teaspoons ground ginger.